Photochemical chlorination process



Aug. 11, 1959 Filed April 16, 1956 D. S. ROSENBERG PHOTOCHEMICALCHLORINATION PROCESS 2 Sheets-Sheet l Vemh A 9 I L"I CII HCl HEseparafior, 1 Polychlorohydmcarbons Zone I; 3 Pr'oducr I 10 8 ll 1' 3 IR le a c t:|on

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F H at l Excfianger I I! 55 I! l i I l' I Hydrocarbon H 2 5 ChionineCivcuIaHna; Siream O 2,899,376 Patented Aug. 11, 1959 PHOTOCHEMICALCHLORINATION PROCESS David S. Rosenberg, Niagara Falls, N.Y., assignorto Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation ofNew York Application April 16, 1956, Serial No. 578,216

"-10 Claims. (Cl. 204-163) This invention relates to a process for thechlorination of aliphatic and alicyclic hydrocarbons. More particularly,this invention relates to a continuous process for the photochemicalchlorination of aliphatic and alicyclic hydrocarbons and partiallychlorinated hydrocarbon derivatives thereof, containing three to eightcarbon atoms in the molecule.

It is known in'the art that the photochemical chlorination of aliphaticand alicyclic hydrocarbons containing three to. eight carbon atoms inthe molecule may be eifectedinchlorinators wherein gaseous hydrocarbonand gaseous-chlorine are introduced continuously into a liquid mixtureof the product in a reaction zone by diffusion means at pointssubstantially removed from one another so as. to minimize thepossibility of an explosion. The usual method of. difiusion provided isthe dispersion of the gaseous feed by use of a porous thimble or afritted glass plate. Mechanical dispersion with a turbo-mixer can alsobe employed. The disadvantages inherent in the use of diiiusers arenumerous. For example,,the poresize of the difiusers normallyused isabout -20 microns, andpores of this size are readily pluggedby tracecontaminants entrained in the gases. Further, gaseous feedsrequire theuse of an elaborate vaporization system operating under pressure toforce the starting material through the small pores ofthe difiuser. Whengaseous reactants are introduced into the photochemical chlorinator,bubbles of gaseous reactants may coalesce and form explosive mixtures.These conditions have imposed severe restrictions on operation ofchlorinators using a feed'system based on'diifusion of; gaseousreactants. Because the risk ofexplosions in using such'reactants is sogreat exceptional precautions must be'taken' in order to avoidexplosions:

It has long been known-in the art that the chlorination of hydrocarbonsmay be-efiected by using liquid reactants. One such processinvolvesintroducing-liquid chlorine directly into a body" of liquid hydrocarbon.or partially chlorinated hydrocarbon under conditions of extremelylowtemperature'in orderto avoid the risk of explosions whichis evengreater-when using liquid'reactants in this manner than when usinggaseous reactants. To my knowledge, the 'riskand danger intheseprocesses has been so greatthat none have been put to use ona'large commercial scale. 7

The principal object-of this invention is to provide a newcontinuousprocess for the photochemical chlorination of aliphatic and'alicyclichydrocarbons and partially chlorinated hydrocarbon derivatives thereof,wherein increasedoverall' efficiency and economy are realized fromimproved operating conditions.

Anotherobject ofthis invention is to provide a safe and economical iprocess which employs" liquid chlorine and liquid hydrocarbon orpartially chlorinated hydrocarbons as reactants-which avoids thewasteful procedure of firstvaporizingythe reactions external to thereactor andin effect recondensing them in the chlorinator.

Another object of this invention is to provide a contiI-iuous processfor photochemical chlorination wherein the mechanical difliculties ofthe prior art are substantially reduced.

Still another object of this invention is to provide a process whereinthe danger of explosion in using liquid reactants is even less than thedanger involved in using gaseous reactants wherein the gaseous reactantsmay coalesce to form explosive mixtures.

I have now found that these and related objects may be accomplished in acontinuous process for the photochemical chlorination of aliphatic andalicyclic hydrocarbons, and partially chlorinated hydrocarbonderivatives thereof, containing three to eight carbon atoms in themolecule inclusive, by the application of new process techniques whereinthe risk of explosion is minimized which comprises maintaining anexternal circulating stream of liquid polychlorohydrocarbon incommunication with a reaction zone containing the main body of theliquid polychlorohydrocarbon. The reactants consisting of liquidchlorine and liquid hydrocarbon are separately injected into saidcirculating stream of liquid polychlorohydrocarbon, while maintainingthe chlorine feed rates and the chlorinator temperature such that 90percent of the reactants entering the said reaction zone are in theliquid phase. The mixture so produced is I passed through an illuminatedzone to eflect chlorination of the organic feed. A portion'of thecirculating stream leaving the reaction zone is withdrawn as product ofthe reaction zone.

The manner in Whichthe process of the present invention is' carried outwill be more clearly understood from the following description of theaccompanying drawings in which Figure 1 isa diagrammatic flow sheetshowing the separate injection of the reactants into a circulatingstream and is one method which may be employed in the performance ofthis process. Figure 2 is a diagrammatic flow sheet showing amodification of the process of this invention wherein the reactants areinjected into separate circulating streams.

Referring to Figure 1: Liquid chlorine 1 and liquid hydrocarbon startingmaterial 2 are separately injected through nozzles into a circulatingstream 3 of liquid polychlorohydrocarb'on having a specific gravitybetween about 1.3 and about 1.8. The external stream is circula-tedthrough the system by means of-pumps 4. The temperature of the reactionmedium in the photochemical clorinator 5 is maintained between about 25degrees and about degrees centigrade by means of an external heatexchanger 6. A portion of the polychlorohydrocar hon is withdrawn in theproduct withdrawal zone 7 to a product recovery zone 8 wherein thedesired product is obtained. Efiluent gases, such as chlorine andhydrogen chloride, are removed from the chlorinator and vented 9 to arecovery system. The photochemical energy is supplied from a mercuryvapor lamp suspended in a light well 10.

Referring to Figure 2: Liquid chlorine 1 and liquid hydrocarbon startingmaterial 2 are injected through nozzles into separate circulatingstreams 3 of liquid polychlorohydrocarbon having a specific gravitybetween about 1.3 and about 1.8. Thestreams are circulated through'thesystem by means of pumps 4. The temperature of the reaction medium inthe photochemical chlorinator 5 is maintained between about 25 degreesand 150 degrees Centigrade by means of external heat exchangers 6. Aportion of the polychlorohydrocarbon is withdrawn in a productwithdrawal zone 7, to a product recovery zone 8 wherein the desiredproduct is obtained. Eflluent gases, such as chlorine and hydrogenchloride, are removed from the chlorinator and vented 9'toa re= coverysystem. The photochemicalenergyis'supplied from a mercury-vapor lampsuspended in a light-well 10.

The above description of the drawings and the following examples furtherillustrate our invention but it is to be understood that the specificdetails given in the drawings and examples have been chosen for thepurpose of illustration and are not intended to limit our inventionexcept as defined in the appended claims.

Example 1 The chlorination apparatus employed to obtain the data of thefollowing example consisted of an eight-inch diameter nickel pipe,seventy inches long, fitted with a jacketed light well assembly whichconsisted of a two inch diameter Pyrex pipe mounted inside a four-inchdiameter Pyrex pipe and supported on the vertical axis of thechlorinator. A 3,000 watt Westinghouse BH-9 mercury vapor lamp suspendedin the light well was used to furnish the photochemical energy for thisexperiment. The chlorinator had a conical bottom section, six and onehalf inches long, wherein the circulating liquid streams entered thechlorinator through a one-inch nickel pipe. A drain valve was providedat the bottom. A two-inch diameter liquid overflow at the top of thechlorinator provided a liquid depth of fifty-six and one-half inches inthe straight section giving a net liquid volume of eight andeight-tenths gallons. Exit gases were withdrawn through a one-inchdiameter nickel pipe mounted nine inches above the liquid overflow. Athermometer well extend- 'ed into the body of the chlorinator formeasuring the liquid temperature.

After the light source had been turned on and had reached normaloperating intensity the circulating stream of polychloropentanes ofspecific gravity 1.670 was started at a maximum flow rate of 22,500pounds per hour. During the usual induction period, the flow rates wereadjusted so that at least 50 percent of the chlorine feed was reacted.In a manner after the foregoing description of the process 110.0 poundsper hour of chlorine and 12.1 pounds per hour of pentane were injectedthrough 0.0625 inch and 0.040 inch diameter orifices, respectively, intothe circulating stream of liquid polychlorohydrocarbon. The ratio ofpolychloropentane circulating rate to the chlorine feed rate was 204.During the reaction period of 9.5 hours, the chlorine to pentane moleratio was kept between 9.0 and 9.5 to 1. The temperature of the reactionmedium was maintained between about 83 degrees and about 88 degreescentigrade. The average temperature drop through the heat exchanger wasdegrees centigrade. Under these conditions 95 percent of the chlorinefeed was in solution in the stream entering the reactor. The hydrogenchloride/ chlorine gas stream leaving the reactor contained about 27percent chlorine. Approximately 80.5 pounds per hour of chlorine wasreacted. A product having a specific gravity of 1.621 at 20 degreescentigrade corresponding to an average composition of C Cl -H wasrecovered.

Example 2 The chlorination apparatus employed to obtain the data of thefollowing example consisted of a thirty-eight inch length of two-inchdiameter Pyrex pipe which was illuminated externally by 6 l00 watt AH-4lamps distributed spirally at uniform intervals (6 inches) along thereaction zone to furnish photochemical energy for the experiments. Adrain valve was provided at the bottom of the chlorinator. A one-inchdiameter liquid overflow was provided at the top of the chlorinator andgave a net liquid volume of 037 gallon. Exit gases were withdrawnthrough a one-inch diameter Pyrex pipe mounted above the liquidoverflow. A thermometer well extended into the body of the chlorinatorfor measuring the liquid temperature.

After the light source had been turned on and had reached normaloperating intensity the circulating stream of polychloropropanes ofspecific gravity 1.633 was started at a maximum flow rate of 1 gallonper minute. Durternal heat exchangers.

ing the usual induction period the flow rates were adjusted so that atleast 50 percent of the chlorine feed was reacted.

In a manner after the foregoing description of the process 1050 gramsper hour of chlorine and 141 grams per hour of propane were injectedthrough one millimeter and 0.5 millimeter diameter orifices,respectively, into the circulating stream of liquidpolychlorohydrocarbon. The ratio of the polychloropropane circulatingrate to the chlorine feed rate was 340. During the reaction period of12.3 hours, the chlorine to propane mole ratio was kept between 4.43 and4.76 to 1. The temperature of the reaction medium was maintained betweenabout 60 degrees and about 65 degrees centigrade. The averagetemperature drop through the heat exchanger was 5 degrees centigrade.Under these conditions 98 percent of the chlorine feed was in solutionin the stream entering the reactor. The hydrogen chloride/ chlorine gasstream leaving the reactor contained about 6 percent chlorine. A producthaving a specific gravity of 1.614 at 20 degrees centigradecorresponding to an average composition of C H Cl was recovered.

The mole ratio of chlorine to hydrocarbon starting material ismaintained between about 3 to 1 and about 12 to 1. The circulatingstream is passed through an irradiated reaction zone to effect thechlorination of the hydrocarbon in a reaction medium of liquidpolychlorohydrocarbon. The reaction is catalyzed by exposing the mainliquid body of polychlorohydrocarbons to the action of actinic lighthaving a wave length from about 3,000 to about 5,000 A. The temperatureof the liquid body of polychlorohydrocarbon employed as a reactionmedium for the chlorination is maintained between about 25 degrees andabout 150 degrees centigrade and preferably between about 50 degrees andabout degrees centigrade by means of external heat exchangers located inthe circulating stream. A portion of the liquid polychlorohydrocarbonstream leaving the reaction zone is withdrawn continuously to maintain aconstant liquid volume in the reaction system.

The liquid reactants are separately injected. through nozzles into thecirculating stream of liquid polychlorohydrocarbon at any point thatwould permit dissolving the reactants externally so that reactants enterthe chlorination zone as a homogeneous solution. Addition of thereactants precedent to the product withdrawal zone would provide aproduct recovery problem. As the reactants are liquid, any method. foradding liquid material is satisfactory. A preferred embodiment is thatshown in the drawings wherein the liquid chlorine and liquid hydrocarbonstarting materials are injected into separate circulating streams ofliquid polychlorohydrocarbons at a fiow point precedent to the pumps toreduce the possibility of forming explosive mixtures should any part ofthe system fail to operate properly. As stated, this procedure isparticularly applicable to hydrocarbons containing three to eight carbonatoms in the molecule. Since the C-3 hydrocarbons have the lowestboiling points, any procedure applicable to these compounds can be usedfor the higher-boiling members of the series.

The photochemical chlorinator contains liquid polychlorohydrocarbonshaving a specific gravity between about 1.3 and about 1.8 as the coolantand diluent for the chlorination of hydrocarbons. The reaction iscatalyzed by exposing the liquid body of polychlorohydrocarbonscontaining the dissolved reactants to the action of actinic light havinga wavelength from about 3,000 to about 5,000 A. The temperature of thereaction medium is maintained between about 25 degrees and about degreescentigrade and preferably betweenabout 50 degrees. and about 125 degreescentigrade by removing the heat of reaction and the heat of the mercuryarc lamps by circulating the polychlorohydrocarbons through ex- The heatload is reduced by about 25 percent by. using liquid feed instead ofgaseous :2; feed. Sinceundesir'edchlorinalysis ofthepolychlorohydrocarbons is initiated at teniperatures about" 150 degreesCentigrade, it"is preferredto maintain the reactionmedium' temperaturebelow about 125; degrees centigrade. The volume of mixedpolychlorohydrocarbons in the chlorinator is kept substantially constantby; continuous withdrawal of liquid polychlorohydrocarbon from theexternal circulating stream as the reactionproceeds.

The flow rate of the circulating stream of liquid polychlorohydrocarbonshaving a specific gravity between about 1.3 and about 1L8 ismaintained-by pumping means, such as a'centrifugal' pump, and isdependent upon-the available heat'ex'ch'anger capacity and the chlorinefeed rate required for the desired production. It is assumed that allheat of reaction is removed in the heat exchanger, as is consistent withsound design principles. The economics of heat exchanger capacitydictate the maximum flow rate While the minimum flow rate is dictated bythe chlorine feed rate required. In the process of this invention atleast 90 percent and preferably substantially all of the chlorine shouldbe in solution on entrance to the chlorinator. Therefore, a minimumratio must be maintained between the rate of circulation of thepolychlorohydrocarbon and the chlorine feed flow rate to maintain thedesired solubility. This minimum ratio is dependent upon thechlorination temperature.

In the following table, the minimum allowable ratio ofpolychlorohydrocarbon circulation rate to chlorine feed rate at variouschlorination temperatures is given for chlorination of n-pentane.

Minimum allowable ratio of polychlorohydrocarbon circulation rate tochlorine feed rate, lb.

Chlorination temperature, C. PCP/lb. C12

90% C15 in solution 1 100% C12 in solution 1 1 Percent 01 in solution atinlet to chlorinator.

The table illustrates that at a circulating rate of 22,500 pounds perhour of polychloropentane, in order to keep 90% of the chlorine insolution, the minimum chlorine feed rates are 281 and 141 pounds perhours at 75 degrees and 95 degrees centigrade, respectively. Forhydrocarbons below pentane in the series somewhat higher circulationrates are needed because of lower hydrocarbon solubility in thepolychlorinated product, and for hydrocarbons above pentane, somewhatlower circulation rates are needed. For example, in Example 2 thepreferred ratio of the polychloropropane circulating rate to thechlorine feed rate is 340, which is somewhat higher than the 210 ratiowhich is the minimum ratio for polychloropentane under substantially thesame reaction conditions.

The reaction between chlorine and a hydrocarbon is especially sensitiveto certain impurities. Therefore, the starting materials should be freefrom harmful inhibitors or materials which may delay or slow down thereaction between the hydrocarbon and the chlorine. Presence of reactioninhibitors such as free oxygen or oxygenated organic compounds in thesystem will inhibit chlorination and they should be eliminated beforestarting chlorination.

An operational hazard arises from the possibility of accumulating anexplosive mixture of chlorine and the hydrocarbon vapor. When thehydrocarbon feed rate exceeds the limit at which all the hydrocarbon isreacted, explosive mixtures of gaseous chlorine and hydrocarbon may bepresent. An excellent control procedure is provided in a circulatingsystem by measurement of the concentration of chlorine in the streamsentering and leaving 6 r the chlorinator, since chlorine consumptioniisalso a meets-'1 ure of the amount of hydrocarbon which is reacted;

From the foregoing specification it is apparent that variousmodifications are possible within the scope of this invention and it' istherefore not to be construed as 11min ing except as defined by theappended claims.

I claim: p

1. A continuous process for the photochemical chl'ori nationof aliphaticand alicyclic hydrocarbons and partially chlorinated hydrocarbonderivatives thereof,', con taining three to eight carbon atoms in themolecule inclu sive, which comprises: maintaining a circulating streamof liquid polychlorohydrocarbon in communication with a reaction zonecontaining the main body of liquid polychlorohydrocarbon said streambeing external to said reaction zone; separately injecting the reactantsconsisting of liquid chlorine and liquid hydrocarbon into saidexternally circulating stream of liquid polychlorohydrocarbon,maintaining the chlorine feed rate and the chlorinator temperature suchthat percent of the reactants entering said reaction zone are in theliquid phase; passing the mixture so produced through an irradiatedreaction zone to effect chlorination of the organic feed; withdrawing aportion of said externally circulating stream leaving the reaction zoneand recovering said portion as a product.

2. A process according to claim 1 wherein the body of liquidpolychlorohydrocarbon maintained as a reaction medium has a specificgravity between about 1.3 and 1.8.

3. A process according to claim 2 wherein the liquid hydrocarbonstarting material is liquid propane and partially chlorinatedhydrocarbon derivatives thereof.

4. A process according to claim 3 wherein the mole ratio of liquidchlorine to liquid propane is maintained between 3 to 1 and about 8 to1.

5. A process according to claim 4 wherein the temperature of the body ofliquid polychlorohydrocarbon maintained as a reaction medium ismaintained between about 50 degrees and about degrees centigrade.

6. A process according to claim 2 wherein the liquid hydrocarbonstarting material is liquid pentane and partially chlorinatedhydrocarbon derivatives thereof.

7. A process according to claim 6 wherein the mole ratio of liquidchlorine to liquid pentane is maintained be-' tween about 3 to 1 andabout 12 to l.

8. A process according to claim 6 wherein the temperature of the body ofliquid polychlorohydrocarbon main-- tained as a reaction medium ismaintained between about. 50 degrees and about degrees centigrade.

9. A continuous process for the photochemical chlori-- nation ofaliphatic and alicyclic hydrocarbons, and par-- tially chlorinatedhydrocarbon derivatives thereof, con-- taining three to eight carbonatoms in the molecule in-- elusive, which comprises: maintainingseparate circulating; streams of liquid polychlorohydrocarbon incommunication with a reaction zone containing the main body of' liquidpolychlorohydrocarbon said stream being external to said reaction zone;separately injecting the reactantsconsisting of liquid chlorine andliquid hydrocarbons intosaid separate externally circulating streams ofliquid polychlorohydrocarbons; maintaining the chlorine feed rates andthe chlorinator temperature such that 90 percent of the reactantsentering said reaction zone are in the liquid phase; passing the mixtureso produced through an irradiated reaction zone to effect chlorinationof the organicfeed; withdrawing a portion from said externallycirculating streams leaving the reaction zone to a product recov-- eryzone, passing the remaining portions of the circulating. streams throughheat exchangers to maintain the temperature of said liquidpolychlorohydrocarbon in said irradiated reaction zone between about 25degrees and aboutv degrees centigrade.

10. A continuous process for the photochemical chlorin-- ation ofaliphatic and alicyclic hydrocarbons, and par-- tially chlorinatedhydrocarbon derivatives thereof, containing three to eight carbon atomsin the molecule inclusive, which comprises: maintaining separatecirculating streams of liquid, polychlorohydrocarbon in communicationwith a reaction zone containing the main body of liquidpolychlorohydrocarbon said streams being external to said reaction zone;separately injectingthe reactants consisting of liquid chlorine andliquid hydrocarbons into .said separate externally circulating streamsof liquid polychlorohydrocarbon so that the reactants entering saidreaction zone are substantially in solution; passing the mixture soproduced through an irradiated reaction zone to effect chlorination ofthe organic feed; withdrawing a portion from a circulating streamleaving the reaction zone to a 5 and about 150 degrees ce nt igradc.

References Cited in the file f thi Paint UNITED S'ITATES PATENTS 102,473,161 McBee et al. June 14, 1949 2,473,162 MeBee et al June 14, 19492,571,901 Lawlor Oct. 16, 1951 Nicolaisen May 8, 1956

1. A CONTINUOUS PROCESS FOR THE PHOTOCHEMICAL CHLORINATION OF ALIPHATICAND ALICYCLIC HYDROCARBONS AND PARTIALLY CHLORINATED HYDROCARBONDERIVATIVES THEREOF, CONTAINING THREE TO EIGHT CARBON ATOMS IN THEMOLECULE INCLUSIVE, WHICH COMPRISES: MAINTAINING A CIRCULATING STREAM OFLIQUID POLYCHLOROHYDROCARBON IN COMMUNICATION WITH A REACTION ZONECONTAINING THE MAIN BODY OF LIQUID POLYCHLOROHYDROCARBON SAID STREAMBEING EXTERNAL TO SAID REACTION ZONE; SEPARATELY INJECTING THE REACTANTSCONSISTING OF LIQUID CHLORINE AND LIQUID HYDROCARBON INTO SAIDEXTERNALLY CIRCULATING STREAM OF LIQUID POLYCHLOROHYDROCARBON,MAINTAINING THE CHLORINE FEED RATE AND THE CHLORINATOR TEMPERATURE SUCHTHAT 90 PERCENT OF THE REACTANTS ENTERING SAID REACTION ZONE ARE IN THELIQUID PHASE; PASSING THE MIXTURE SO PRODUCED THROUGH AN IRRADIATEDREACTION ZONE TO EFFECT CHLORINATION OF THE ORGANIC FEED; WITHDRAWING APORTION OF SAID EXTERNALLY CIRCULATING STREAM LEAVING THE REACTION ZONEAND RECOVERING SAID PORTION AS A PRODUCT.